Solution and solid state nuclear magnetic resonance spectroscopy are being used along with circular dichroism, microelectrophoretic mobility, fluorescence spectroscopy, differential scanning calorimetry, mass spectrometry and computer modelling to study the structure of peptides and small proteins in solution and in the bound state. Proteins which have been investigated include the homeodomain (DNA binding domain) of the NK-2 protein encoded from the homeobox gene of Drosophila melanogaster and the third variable domain of gp120 from HIV-1. Studies are also in progress on an antigenic peptide bound to a monoclonal antibody and a peptide epitope bound to major histocompatibility complex.